This invention relates generally to land vehicles and more particularly to wheelchairs. Most particularly, the invention relates to a center-of-gravity tilt-in-space wheelchair having a seat assembly supported relative to a base by a rocker that has a curvature the focal point of which is coincident with the center of gravity of the wheelchair occupant so that the center of gravity of the wheelchair occupant remains at a fixed location during tilting.
Tilting wheelchairs are well known. Such wheelchairs are typically used in highly dependent or geriatric care, wherein the ability to reposition a wheelchair occupant in various angular positions is beneficial to the occupant's health and daily routine. Tilting a wheelchair occupant relieves pressure to the wheelchair occupant's ischial tuberosities (i.e., the bony prominence of the buttocks). Continuous pressure to the wheelchair occupant's ischial tuberosities, which is applied when the wheelchair occupant remains in a single seated position, can cause the development of decubitus ulcers (i.e., pressure sores). For wheelchair occupants with severe kyphosis (i.e., curvature of the spine), seated tilting may allow the occupant to look forward and interact with their surroundings. Tilting may also be beneficial to assist with proper respiration and digestion.
Some wheelchair occupants require attendant care, wherein an attendant is responsible for positioning the wheelchair seat angle, often changing the angle on a prescribed schedule. The ability to tilt the wheelchair occupant offers the occupant a variety of positions that accommodate their daily schedule, including, for example, an anterior tilt for eating at a table and posterior tilt for resting.
Conventional tilting wheelchairs consist of a seat frame that is pivotally mounted to a base frame so that the seat frame tilts to reposition the wheelchair occupant. The pivot axis is typically mounted between the base frame and seat frame, towards the rear of the seat and away from the occupant's center of gravity. Tilting the occupant involves lifting or lowering his or her center of gravity and therefore requires effort on the part of the attendant. Mechanisms, such as springs or gas cylinders, are often employed to assist in tilting the occupant. Typically, levers are attached to handles on a tilting wheelchair. The levers allow an attendant to release a locking mechanism, change the tilt angle by pushing or pulling on the handles, and engage the locking mechanism, which fixes the tilt angle.
Tilting in conventional tilt wheelchairs may invoke a reaction on the part of the occupant who experiences the sensation of being tipped over. The occupant experiences a sensation of being pitched off balance during tilting. Conventional tilt wheelchair designs involve translation of the wheelchair occupant's center of gravity during tilting. Significant effort on the part of the attendant may be required to tilt the wheelchair occupant when the occupant's mass translates during tilting. Moreover, conventional tilt wheelchairs require large base frames and anti-tip devices because tilting the chair displaces the occupant's center of gravity fore and aft over the wheelbase, potentially placing the wheelchair off balance.
What is needed is a wheelchair that does not evoke the sensation of being tipped over; that requires minimal effort on the part of the attendant to tilt (i.e., no lifting or lowering of the wheelchair occupant's center of gravity should be required to tilt the wheelchair); does not affect weight distribution between the front and rear wheels; and that is limited to pure rotation (i.e., the only effort required is to overcome friction within the system), thus eliminating the need for springs or gas cylinders to assist tilting.